Method of storing oxygen



April 16, 1968 R. A. RUEHRWEIN ETAL 3,378,351

METHOD OF STORING OXYGEN Filed Oct. 24, 1961 4 Ddschary: region.

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United States Patent 3,378,351 METHOD 0F STORING OXYGEN Robert A. Ruehrwein, Clayton, Mo., and .loseph S. Hashman, Evans City, Pa., assignors to the United States of America as represented by the Secretary of the Army Filed Get. 24, 1961, Ser. No. 147,378 7 Claims. (Cl. 23-315) This invention relates to a process for the storage of oxygen. More particularly it relates to a method of combining oxygen gas with other compounds and solidfying the product into a blend much more stable than solidified oxygen itself.

Oxygen is conventionally stored in its liquid form. However, it cannot be stored at a temperature higher than its boiling point unless it is kept under high pressures. In order to maintain this high pressure, heavy equipment such as metal storage tanks, safety devices, etc. must be used. Since this invention requires no pressure, such equipment is eliminated.

Therefore, an object of this invention is to provide a process which will allow oxygen to be stored without the use of high pressures or the equipment necessary therefor.

A further object of this invention is to provide a means whereby oxygen may be stored in a stable manner at low temperatures.

Another object of the invention is to provide a supply of oxygen in a solid, stable form, which upon subsequent vaporization, provides a ready source of oxygen for any purpose for which it is conventionally used.

The foregoing and other objects and advantages will become apparent from the following detailed description of the invention.

In accordance with this invention, oxygen gas is blended with another gaseous material, preferably one of the following: water vapor, nitrogen dioxide (or nitrogen tetroxide) and olefins such as ethylene or isobutylene. Immediately thereafter the mixed blend is subjected to extremely low temperatures of about 4.2 K. A solidified product is formed which is a complex of molecular oxygen and another compound. The solidified product is then warmed to a temperature of from about 66 K. to about 77 K. in order to allow the uncomplexed oxygen to be pumped from the solidification zone. The remaining solid complexed material is much more stable than pure solidified oxygen and consequently may be stored indefinitely at much higher temperatures, up to 200 K. When it is desired to obtain oxygen gas from the solidified complexed material, it is merely necessary to raise the temperature of the material to a point at which oxygen gas is evolved therefrom.

The various gases used in this process are obtained from any well known source such as from commercial supplies thereof and are essentially pure.

More specifically, with particular reference to the single figure of the drawing, oxygen gas, usually obtained directly from a cylinder (not shown), is introduced through a supply tube 1 and controlled by means of a stopcock 2. It is throttled into a Pyrex tube 3 open at its lower end and having a Y connection with another supply tube 15. The oxygen gas flows out of the lower end of tube 3 into the lower part 6 of a Pyrex cylinder 5. The lower part of this cylinder is immersed in liquid helium. It is also equipped with a vacuum pump connection 7 which may be in turn connected with a vacuum pump (not shown) when it is desired to remove gases from the cylinder 5. The lower part 6 of Pyrex cylinder which has been immersed in liquid helium acts as a trap or condenser by freezing out all gases and thus constitutes, in eifect, a high speed pump for maintaining the flow of gas toward it.

Surrounding the Pyrex tube 3 is another Pyrex tube 8,

3,378,351 Patented Apr. 16, 1968 also open at its lower end and having hollow walls 9. The additional gas with which it is desired to blend the oxygen gas is supplied from a source (not shown) through either tube 10 or tube 15. If the additional gas is supplied through tube 10, it is then drawn down tube 8 into the lower part 6 of cylinder 5 by the vacuum created therein by the action of the liquid helium constantly freezing out all gases. The blending of the oxygen gas and the additional gas then takes place in the lower part 6 of cylinder 5 wherein it is almost immediately solidified. When the additional gas is supplied through tube 15 it is blended with the oxygen gas at the Y connection of Pyrex cylinder 3 and tube 15. The two gases together then are drawn down Pyrex cylinder 3 and out the lower end thereof into the lower part 6 of Pyrex cylinder 5 wherein they are solidified.

In order to prevent condensation or solidification of the gases at temperatures much above 4.2 K., Pyrex tubes 3 and 8 are kept at a relatively high temperature, for instance, room temperature. This temperature is maintained by forcing a relatively warm gas such as helium or nitrogen into the hollow walls 9 of tube 8. The introduction of such a sheath of warm gas extending considerably below the liquid helium level causes but a slight heat input. However, by this means the gases pass abruptly from a relatively high temperature to the extremely low temperature of the lower part 6 of Pyrex cylinder 5 and accumulate in solid form in this area.

The liquid helium bath may be insulated from the outside temperature by an additional bath of liquid nitrogen in order to reduce the amount of liquid helium required to maintain the lower part of cylinder 5 at a very low temperature. The helium and nitrogen baths are contained in Dewar flasks 11 and 12, respectively, which can be raised and lowered by means of a screw elevator (not shown) in order to vary the temperature in the lower end of cylinder 5. The silvered Dewar flasks 11 and 12 are provided with strip windows 13 and 14, respectively, to allow observation of the solidified material which is deposited at the bottom of Pyrex cylinder 5. The level of the liquid helium is maintained around the lower end of Pyrex cylinder 5 by slowly raising the Dewar flasks as the helium boils away. This prevents unnecessary excessive cooling of the Pyrex entrance tubes 3 and 8.

Following the blending of the oxygen gas with an additional gas and the subsequent solidification thereof, the lower end 6 of cylinder 5 is warmed to a temperature of from about 66 K. to about 77 K. by lowering the Dewar flasks 11 and 12. Control of the elevation of the Dewar flasks gives very good temperature control and it is possible to warm or cool the solidified product at will or hold it at any desired temperature for hours. As the solidified product is warmed to the aforementioned tempera ture, the uncomplexed oxygen becomes gaseous again and is removed by a vacuum pump (not shown) through connection 7. This oxygen gas may be recovered and then returned to the original oxygen supply in order to be used in the process again. The remaining solid material is, of course, the complex of solidified oxygen and an additional solidified gaseous compound. The oxygen may be conveniently stored in the complex for an indefinite period as long as its temperature remains below the decomposition point thereof. A ready supply of oxygen gas is obtained by merely raising the temperature of the solid complexed product above its decomposition point.

In order that the invention may be further illustrated, the following are examples of typical embodiments of the invention.

Example I A mixture of nitrogen dioxide gas and oxygen gas was solidified at the temperature of liquid helium (about 4.2

3 K.) in the trap formed by the lower part 6 of Pyrex cylinder 5. After warming to 77 K. and pumping off the uncombined oxygen gas, it was found that additional oxygen gas was evolved from the solidified complex product of nitrogen dioxide and oxygen at temperatures approaching and including 124 K., in a reversible manner, and in the ratio of one mole of oxygen to 6.6 moles of N Example 11 A mixture of water vapor and oxygen gas was solidified as in Example I. Again, after warming to 77 K. and pumping off the uneombinecl oxygen gas, it was found that additional oxygen gas was evolved from the solidified complex product of water vapor and oxygen at temperatures approaching and including 150 K. and in the ratio of one mole of oxygen to 10.5 moles of water.

Example III A mixture of isobutylene gas and oxygen gas was also solidified as in Example 1. After warming to about 72 K. and pumping off the uncombined oxygen gas, it was found that additional oxygen gas was evolved from the solidified complex product of isobutylene and ox gen at a temperature around 130 K. and in a ratio of one mole of oxygen to 27 moles of i-C H Example IV A mixture of ethylene gas and oxygen gas was also solidified as in the previous examples. After warming to about 66 K. and pumping off the uncombined oxygen gas, it was found that additional oxygen gas was evolved from the solidified complex product of ethylene and oxygen at a temperature of about 86 K. in a reversible manner and in the ratio of one mole of oxygen to 7.6 moles of C2H4.

While the foregoing embodiments have been set forth in considerable detail, it is to be distinctly understood that many modifications and variations will naturally present themselves to those skilled in the art without departing from the spirit of this invention or the scope of the appended claims.

Having thus described the invention, what is claimed is:

1. A method for the preparation of a complex compound capable of storing oxygen at normal pressure comprising, blending oxygen gas in a vacuum with a material selected from the group consisting of water vapor, nitrogen dioxide gas, ethylene gas and isobutylene gas, solidifying by freezing the resulting blend to obtain a complexed product thereof, warming said product to a temperature between 66-77 K. to render any uncomplexed oxygen gaseous for removal and utilizing the final solidified complexed product as a safe means of storing the complexed oxygen at normal pressure as long as the temperature of the solid product is maintained below 86 K.

2. A method of safely storing oxygen at normal pressures combined in a complex compound comprising, blending in a vacuum oxygen gas with a material selected from the group consisting of water vapor, nitrogen dioxide gas, ethylene gas and isobutylene gas, solidifying the blended gas by freezing at a temperature of approximately 4.2 K. to obtain a complexed product thereof, warming said product to a temperature in a range of 66 K. to 77 K. to render any uncomplexed oxygen gaseous for removal, utilizing the solidified complex product as a safe storage of oxygen at normal pressure by maintaining the temperature below 86 K. and retrieving the oxygen for use from the solidified complex product by raising the temperature to a range of 124 K. to 150 K.

3. A solid complexed compound for the safe storage of oxygen at normal pressure and at temperatures below 86 K. consisting of a stable solidified combination formed of oxygen and a material selected from the group consisting of water vapor, nitrogen dioxide gas, ethylene gas and isobutylene gas and free of uncomplex oxygen.

4. A solid complexed compound for the safe storage of oxygen at normal pressure and at temperatures below 77 K. consisting of a stable solidified compound of solidified oxygen and solidified nitrogen dioxide gas free of uncomplexed oxygen and yielding a supply of oxygen gas at temperatures approaching and including 124 K.

5. A solid complexed compound for the safe storage of oxygen at normal pressure and at temperatures below 77 K. consisting of a stable solidified combination of frozen water vapor and solidified oxygen gas free of uncomplexed oxygen and yielding a supply of oxygen gas at temperatures approaching and including 150 K.

6. A solid complexed compound for the safe storage of oxygen at normal pressure and at temperatures below 72 K. consisting of a stable solidified combination of solidified oxygen and solidified isobutylene gas free of uncomplexed oxygen and yielding a supply of oxygen gas at temperatures approaching and including K.

7. A solid complexed compound for the safe storage of oxygen at normal pressure and at temperatures below 66 K. consisting of a stable solidified combination of solidified oxygen gas and solidified ethylene gas free of uncomplexed oxygen and yielding a supply of oxygen gas at temperatures approaching and including 86 K.

References Cited UNITED STATES PATENTS 2,892,766 6/1959 Broida et a1. 204164 3,062,730 11/1962 Ruehrwein 204176 3,217,503 11/1965 Mitchell et a1 62-1 XR 1,680,873 8/1928 Lucas-Girardville 62-47 2,217,678 10/1940 Goosmann 621 2,939,778 6/ 1960 McKinley 62-48 OTHER REFERENCES Stackelberg, Zeitschrift for Elektrochemie, vol. 58, pp. 104-109 (1958).

MILTON WEISSMAN, Primary Examiner. ROBERT A. OLEARY, Examiner.

M. L. MOORE, Assistant Examiner. 

1. A METHOD FOR THE PREPARATION OF A COMPLEX COMPOUND CAPABLE OF STORING OXYGEN AT NORMAL PRESSURE COMPRISING, BLENDING OXYGEN GAS IN A VACUUM WITH A MATERIAL SELECTED FROM THE GROUP CONSISTING OF WATER VAPOR, NITROGEN DIOXIDE GAS, ETHYLENE GAS AND ISOBUTYLENE GAS, SOLIDIFYING BY FREEZING THE RESULTING BLEND TO OBTAIN A COMPLEXED PRODUCT THEREOF, WARMING SAID PRODUCT TO A TEMPERATURE BETWEEN 66*-77*K. TO RENDER ANY UNCOMPLEXED OXYGEN GASEOUS FOR REMOVAL AND UTILIZING THE FINAL SOLIDIFIED COMPLEXED PRODUCT AS A SAFE MEANS OF STORING THE COMPLEXED OXYGEN AT NORMAL PRESSURE AS LONG AS THE TEMPERATURE OF THE SOLID PRODUCT IS MAINTAINED BELOW 86*K.
 3. A SOLID COMPLEXED COMPOUND FOR THE SAFE STORAGE OF OXYGEN AT NORMAL PRESSURE AND AT TEMPERATURES BELOW 86*K. CONSISTING OF A STABLE SOLIDIFIED COMBINATION FORMED OF OXYGEN AND A MATERIAL SELECTED FROM THE GROUP CONSISTING OF WATER VAPOR, NITROGEN DIOXIDE GAS, EHTYLENE GAS AND ISOBUTYLENE GAS AND FREE OF UNCOMPLEX OXYGEN. 